This invention pertains to coal catalytic hydrogenation to produce hydrocarbon liquid and gas products, and particularly to a coal hydrogenation process in which ash from the coal is agglomerated in and withdrawn from an ebullated bed catalytic reactor.
In conventional catalytic coal liquefaction and hydrogenation processes which use high pressure hydrogen to produce hydrocarbon liquid and gaseous products, the separation of fine particles of ash from the coal-derived liquid product is a major problem. Such ash separation is usually accomplished by passing the coal-derived liquid through a liquid-solids separation step such as hydroclones, filters, or to a solvent precipitation step. However, such ash separation processes are expensive and troublesome to use, and improved procedures for more direct removal of ash from coal-derived liquids have been sought. Although it is known to withdraw small portions of used catalyst particles from ebullated catalyst bed reactors used in coal hydrogenation processes, as generally disclosed by U.S. Pat. No. 3,398,085 to Engle and U.S. Pat. No. 3,519,555 to Keith, et al., agglomeration and selective withdrawal of a significant portion of the ash particles from the catalytic reaction zone has not previously been considered feasible.